diff -rubp asterisk-13.6.0.orig/channels/chan_sip.c asterisk-13.6.0.fixed/channels/chan_sip.c
--- asterisk-13.6.0.orig/channels/chan_sip.c	2015-10-09 23:48:48.000000000 +0200
+++ asterisk-13.6.0.fixed/channels/chan_sip.c	2015-12-04 14:49:34.250077514 +0100
@@ -4746,6 +4746,11 @@ static int sip_queryoption(struct ast_ch
 	struct sip_pvt *p = (struct sip_pvt *) ast_channel_tech_pvt(chan);
 	char *cp;
 
+	if (!p) {
+		ast_debug(1, "Attempt to Ref a null pointer. Sip private structure is gone!\n");
+		return -1;
+	}
+
 	sip_pvt_lock(p);
 
 	switch (option) {